Heat-treatable, age hardenable aluminum alloys, such as 2xxx, 6xxx and 7xxx aluminum alloys, are used for the production of panels in vehicles such as automobiles. These alloys are typically provided to an automotive manufacturer in the form of an aluminum sheet in a ductile T4 state (or temper) to enable the manufacturer to produce the automotive panels by stamping or pressing. To produce functional automotive panels meeting the required strength specifications, the manufacturer has to heat treat the automotive panels produced from an aluminum alloy in T4 temper to increase their strength and convert the aluminum alloy into T6 temper. In automotive manufacturing, the heat treatment is often accomplished for outer automotive panels during a paint bake process of the assembled motor vehicle body. For inner automotive parts, a separate heat treatment is often required, referred to as Post Forming Heat Treatment (“PFHT”).
Current processes used in the motor vehicle industry for heat treatment of pressed aluminum automotive panels to increase their strength possess notable disadvantages. Heat treatment during the paint bake cycle of assembled motor vehicle bodies requires paint lines with sufficient heat power to achieve the required temperature, particularly in thick and inner structural elements of a car. Paint bake heat treatment is difficult, particularly for inner automotive panels, because the outer panels act as a heat shield, resulting in uneven hardening of different parts of a motor vehicle body. For example, during a typical paint bake cycle, the outer panels may be exposed to a temperature of 170 to 185° C. for about 20 minutes, which leads to their “bake” hardening. However, during a similar paint bake cycle, the floor panels in an assembled automobile body are exposed to a temperature of only 130 to 160° C. for 10 to 15 minutes, which does not result in significant hardening. Although effective, PFHT is inefficient. For example, a heat treatment at about 225° C. for approximately 30 minutes may be required to get full T6 temper in panels through PFHT. PFHT leads to high energy costs, is time consuming and requires expensive modifications of the production lines. In other words, PFHT adds significant costs to and lengthens motor vehicle production cycles.